Burner ignition system



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May 5, 1970 G. J. GRANIERI BURNER IGNITION SYSTEM Filed April 1. 1968 2 Sheets-Sheet 2 INVENTOR.

GEORGE J. GRANIERI x CM@ ATTORNEY United States Patent Office 3,510,237. Patented May 5, 1970 3,510,237 BURNER IGNITION SYSTEM George J. Granieri, Piscataway, NJ., assignor to American Standard Inc., New York, N.Y., a corporation of Delaware Filed Apr. 1,1968, Ser. No. 717,587 Int. Cl. F23n 5/08 U.S. Cl. 431-79 15 Claims ABSTRACT F THE DISCLOSURE This invention covers a direct burner ignition system for heating or cooling or other air conditioning equipments. The system includes an electrical spark producing device for igniting the incoming fuel, a flame sensor for observing the color of the flame of the ignited fuel, a protective apparatus for responding to the color of the flame and for rendering the system inoperative when the color of the flame is different from a predetermined color (such as blue). If the flame sensor includes a cadmium sulphide cell, the protective apparatus will respond instantly to said different predetermined color. If a flame outage occurs, re-ignition will be provided within about eight-tenths of a second. The system includes fail-safe features to render the system inoperative due to any failure of the equipment.

This invention relates to electrical ignition systems and, more particularly, to electrical ignition systems employing solid state circuitry. Still more particularly, this invention relates to ignition systems for air-conditioning equipments, i.e. heating systems or cooling systems and the invention is especially applicable to ignition systems which have heretofore been controlled principally by a conventional pilot light.

Prior forms of pilot light ignition systems have incorporated safety features for the protection not only of the building in which the system is located but also of the personnel within the building. As is well known, however, the pilot light may fail to operate or, if it does operate, it may, for some reason, be extinguished. Should it fail to be extinguished when this is necessary to prevent the system from operating, damage may be done to the system by the unwanted heat produced. On the other hand, should the pilot light fail to operate when it is expected to operate, raw gas or other ignition material may emanate from the boiler gas main and, without the presence of a pilot light, a highly dangerous condition, that is, an explosive condition, may be present. Such situations are particularly dangerous when the pilot light system is on the roof of a building, for example, where the pilot light may be blown out by a mild blast. In such cases if the raw gas continues to emanate from the gas line, as often happens, the hazard would be indeed great to life and property in the vicinity.

It is therefore one of the main objects of this invention to produce an ignition system which is substantially safe at all times even when operating without a Apilot light. This is accomplished, in accordance with this invention, by assuring that when the lburner is receiving gas, the required initiating light or spark will be present when required but, on the other hand, when the gas line is interrupted, the initiating light or spark will be extinguished or, when the initiating light or spark is extinguished, the gas line will be interrupted and so maintained.

Another of the features of this invention relates to the employment of a flame sensor which will be used to distinguish between a yellow llame and a blue flame so that the system will continue to operate normally while a blue flame is present but, when a yellow llame is developed, the system will be rendered inoperative.

Another of the primary features and objects of this invention is to devise a direct burner system, that is, a system that is free of any pilot light, which is simple and inexpensive to build and maintain and fail-safe under essentially all conditions.

These and other objects and the many features of this invention will be more apparent from the following description explaining some of the objects and features of this invention, when read in connection with the accompanying drawing, in which FIG. l schematically illustrates a block diagram merely to explain the principal objects and features of the invention, and FIG. 2 illustrates a wiring diagram showing in more detail a form of circuitry which may be used in carrying out the objects and features of this invention. Similar reference characters will be employed throughout this application to refer to the same or similar parts.

Referring to both figures of the drawing, and especially to FIG. 1 of the drawing, TH designates a thermostat of any well-known type which is employed to close the circuit when there is a demand for heat. GS designates a gas pressure switch which maybe of any well-known type and which is normally closed when there is suflicient gas pressure in the mains through which gas is furnished to the system. IN designates a source of voltage, usually about 220 volts and 60 Hz., which is employed to supply power to the system. SD designates a spark device which may be any I"well-known arrangement for producing a spark to ignite incoming gas supplied through a pipe to which the gas pressure switch GS is coupled FS designates a flame sensor which may be any flame sensing device, but it is preferably a cadmium sulphide device which is capable of detecting the presence of a gas flame. Obviously any device responsive to a flame would be suitable for this general purpose, such as a flame switch or a high temperae ture thermistor having a negative temperature coeflicient. The spark device SD may include a transformer T2 so that it may be connected to the ignition circuit GC and to the rest of the system. A transformer T3 connects the thermostat TH and the gas pressure switch GS to the rest of the system. No conventional pilot light will be required and none will be employed anywhere in the system whether or not it is housed indoors or outdoors.

lIn general, when there is a demand for heat, the thermostat TH will be closed and, if there is suflicient gas pressure in the gas mains, the switch GS will be closed or remain closed if it was initially closed. A signal will then be transmitted to the transformer T3 through a normally closed gas valve GV and a fan timer FT, and the signal will also be transmitted to the primary safety control network SC and the network SC will in turn transmit a corresponding signal to the DC power control network CN which in turn will relay a signal to the primary safety switch PS. This will then activate the motor control network MN which in turn energizes the motor MO which is any suitable combustion blower motor. The closure of the primary safety switch PS will then energize the ignition circuit GC. The ignition circuit GC will then produce a pulse or a series of pulses which will activate the spark device SD. Without such pulses the spark device SD cannot and will not operate.

l When the motor MO reaches a predetermined speed, a centrifugal switch CS of well-known type will be closed. The closure of switch CS in turn will open the circuit of the gas valve GV and at the same time energize and operate the fan timer FT. The gas valve GV is preferably positioned adjacent to the spark device SD. Upon the closure of the gas valve GV, the gas flowing therethrough will be ignited by the sparks generated by the spark device SD producing a flame in the usual manner.

If there is proper combustion in the burner equipment, a blue flame will be produced by the ignited gas and the blueness of the flame will be detected by the flame sensors FS. If the flame is not satisfactory, for example, it. it is of a yellow coloration, the flame sensor FS will characteristically respond thereto. In either case, the flame coloration will, in general, be detected by the flame detector network FN. The response of the flame detector network FN will in turn be communicated to the ignition circuit GC. Simultaneously with the operation of the flame detector network FN, the primary safety timer ST will also become deenergized.

If the ame at the spark device SD is yellow instead of blue, the flame detector network FN will respond to such a coloration but it would inhibit the primary safety control network SC from being operated. As will be explained hereinafter, the flame controlling mechanism will then go into oscillation for a limited time period. That is, the flame initiated by the spark device SD will go on and off repeatedly and, in due course, the flame will be turned off by the mechanism and remain turned off until the secondary safety switch SS is reset.

If there is no longer a demand for heat, the circuit of thermostat TH will be opened in the usual way. The primary safety switch PS, previously closed, will remain closed. As soon as the thermostat TH opens, both the gas valve GV and the timer FT will be deenergized. Hence, the gas valve GV will be closed so that no gas will thereafter enter the region where the spark device SD is positioned. Consequently, the flame of the burner will be turned off and remain turned off. The flame sensor FS will promptly detect the absence of any ame. The flame sensor FS will respond so as to energize the flame detector network FN which in turn will reactivate the ignition circuit GC to transmit energy to the spark device SD. A continuous spark will again be produced by the spark device SD and the device SD will be ready for the next call for burner operation. At the same time, moreover, the safety switch PS will be activated and, after a predetermined interval of time, such as seconds, the primary safety timer ST will transmit a pulse to the primary safety control network SC. This pulse -will inhi-bit the primary safety control network SC from operating or remaining operated and this in turn will inhibit the DC power control network CN from remaining operated. Thereupon, the primary safety switch PS will be opened. At this point in the operation of the system, the motor MO will be turned off. The opening of the primary safety switch PS will instantly open the ignition circuit GC so that no further sparking will be produced by the spark device SD. The complete ignition system is now disabled during this part of the cycle and it is incapable of igniting any incoming gas.

Now let us consider the operative characteristics of the system in the event that the gas valve GV, for example, is restricted so it is unable to supply a suicient amount of gas in the region of spark device SD. Assume here that there is a demand for heat, whereupon the thermostat TH has been closed. Assume also that the gas pressure switch GS is closed because there is sufficient gas pressure in the gas main. Under these conditions, however, the motor MO will nevertheless be operated and its centrifugally controlled switch CS will be closed. Hence the ignition circuit GC will be energized. lIf no flame should appear adjacent to the spark device SD because insufficent gas is permitted to traverse the gas valve GV due to the restriction therein, the absence of flame will be detected promptly by the flame sensor FS. If a photocell, such as a cadmium sulphide cell, is employed, the absence of the flame at the spark device SD will be detected substantially instantly, i.e., within about 0.8 seconds and, within a predetermined period of time such as 10 seconds, the primary safety timer 'ST will initiate a pulse at its output. This in turn will open the primary safety switch PS. The electrical system will be locked in this position to prevent firing of the gas by the spark device SD. If desired, another run may be started by reopening the contacts of the thermostat TH and allowing its contacts to re-close to operate the system if a sufficient supply of gas can be furnished. The system is capable of being restarted if normal conditions return. It is a feature of this invention to lock the system against gas firing if an insufficiency develops but it is entirely possible to restart the mechanism when conditions are normalized merely by re-setting the thermostat TH.

It will be noted that the primary safety switch PS is operated and held closed during a normal mode of operation of the system and is opened at the end of a heating cycle. Upon a failure occurring in the DC power control network CN or in the primary safety control network SC or in the primary safety timer ST or in the flame detector FN, the primary safety switch PS may be held closed even though there is no demand for heat. When the primary safety switch PS is closed, it is impossible for the ignition circuit GC to become deenergized and the safety heater coil HC would eventually maintain the secondary switch SS open, thereby removing power from the system.

The switch SS is preferably a bimetallic device, for example, .ETA Safety Switch No. 44-8000. The safety heater coil HC is merely a control device which, after it is energized, will actuate the switch SS to open its path. The opening of switch SS will completely remove power from the source IN from the system. The system may only be restarted by reclosing the switch SS.

Another feature of this invention is its fail-safe character relative to the flame sensor FS. Should the flame sensor FS become short-circuited, for example, prior to any demand for heat, then upon the closure of the switch TH due to a demand for heat, a signal will be transmitted to the primary safety control network SC. However, the flame detecting network FN will prevent the primary safety control network SC from becoming energized because the flame sensor FS is shorted, Under these conditions, that is, conditions in which the flame Sensor FS is shorted, the system Iwill remain disconnected.

On the other hand, if the flame sensor FS were opencircuited (rather than shorted), the primary safety timer ST will be enabled, hence the timer ST will generate a pulse and thereby turn off the system as already explained.

FIG. 2 shows the more detailed circuitry and the general layout of the equipment to carry out the principal features of the invention as already outlined in connection with the description of the schematic block diagram of FIG. l. In the FIGURE l arrangement, semi-conductive devices are employed.

The FIGURE 2 arrangement embodies a pluarality of semi-conductive devices, some of which are sometimes called active devices, and all of these semi-conductive devices, except transistor Q1, are normally non-conducting as will be explained hereinafter. Inasmuch as transistor Q6 is non-conducting, the transistor Q1 receives rectified base current from a power circuit which is coupled to a secondary winding of the transformer T1. The circuit for the rectified current includes the diode rectifier D1 and the capacitor C1, and the diode rectifier D1 is connected to the base of transistor Q1 by resistor R1 so that the rectified current can flow to the base in the forward direction. The transistor Q2 may preferably be a thyristor, as shown, and it will receive no gate current through resistor R3. The absence of gate current is due to the fact that the collector and emitter electrodes of transistor Q1 are essentially at .ground'potentiaL Transformer T3 has a low exciting current and therefore produces a voltage across resistor R22 which is too small in magnitude to trigger the device Q13 which may be, preferably, a silicon unilateral switch. The device Q13 is connected across resistor R22 via the gas valve GV, resistor RS, diode D6, resistor R16, resistor R14, and resistor R13. If the device Q13 is nonconductive, the system will remain normally unoperated before there is any demand for heat.

If there is a demand for heat, the circuit of thermostat TH will be closed and, if there is suicient gas pressure in the gas supply main, the switch GS will also be in its normal or closed position. Under these conditions the secondary winding of transformer T3 will be converted into a low impedence. When this occurs, a suicient voltage will be produced across resistor R22 and a higher voltage will be applied to device Q13 to render it conductive. The capacitor `C5 will then be charged to a positive voltage over a circuit including the secondary windings of transformers T1 and T3, gas valve GV, device Q13, resistor R5, diode D6, resistor R16, capacitor C5 and ground. The capacitor C5 may now be treated as though it were a source of DC power. It supplies power for the primary safety control network SC which includes the transistor Q6 and Q7. Capacitor C5 will also be a source of power for the primary safety timer circuit ST of which it may be a component and also for the llame detector network FN. When the voltage across resistor R13 reaches a predetermined value, such as 6 volts, the emitter to base junction of transistor Q7 (wich is wired and poled so as to act as a blocking diode) will break down and thereby allow current to flow to the base of transistor Q6 to render transistor Q6 conductive. When this happens, as previously suggested, the transistor Q1 will be turned off because its base electrode will then ybe clamped to ground through the collector and emitter junction of transistor Q6. As soon as transistor Q1 is turned O, current will be supplied to the gate of the device Q2 which is essentially a bilateral switch, current being supplied to the gate of device Q2 over the circuit which extends from the secondary of transformer T1 and includes diode D1, resistors R2 and R3 and ground. Hence, transistor Q2 is rendered conductive to AC current. At the same time, current will also be supplied to the gate of the device Q3 rendering it conductive, the circuit including the diode D1, the resistor R2, resistor R6 and the gate electrode of device Q3. As soon as the device Q3 becomes conductive, the AC voltage of the source IN will be applied to the motor MO. When the impedance of device Q3 is substantially reduced, it will permit AC current to ow from the primary winding of transformer T1 through the motor MO to operate motor MO. As the motor MO reaches a predetermined speed, the centrifugal switch CS, which may be mounted on the shaft of the motor MO, closes its contact. When this happens a prede termined AC voltage will be supplied to the gas valve device GV and to the fan timer FT to maintain them in operation.

When the thyristor device Q2 becomes conductive, the ignition circuit GC and the heater coil HC will be energized from the input cirucit IN, the interconnected circuit including the diode D3, the winding of heating coil HC the resistor R21 and its shunt capacitor C3, and the low impedance path to ground through the conductive device Q2. It will be observed that there is also a parallel circuit across resistor R21 and capacitor C3 and this parallel circuit includes the primary winding of transformer T2 and the device Q5. The diode D3 provides half wave current for the ignition circuit GC and for the heater coil HC through the primary winding of transformer T2. The voltage across the primary winding of transformer T2'- produces a higher voltage through the secondary winding of transformer T2. The spark device SD ignites the gas supplied through the `gas valve GV. It is noted that transformer T2 produces a secondary winding voltage, the eifective voltage depending on the time rate of change of current in the primary circuit. Due to the high rapidity of the response of device Q5, the secondary voltage pulses will be of relatively high voltage.

It is noted that the two capacitors C2 and C3 of the ignition circuit GC are charged at different rates, the capacitor C3 being charged rapidly while the capacitor C2 is charged at a much slower rate because of the high impedance introduced by resistor R8. When the voltage across the capacitor C2 reaches the breakdown voltage of device Q4, capacitor C2 discharges over a circuit which includes resistor R9, the device Q4, and the gate controlled device Q5. The discharge current turns the device Q5 on. At the same time the capacitor C3 will discharge over a path which includes the primary winding of transformer T2 and device Q5.

If proper combustion is taking place in the main burner, the resultant llame adjacent to the spark device SD will be what is recognized as a blue flame. The flame sensor FS and the resistor R20 will be in a circuit introducing suicient voltage to break down the emitter to base junction of transistor Q12 which is arranged as a zener diode and is part of the iiame detector network FN. The interconnected circuit will include the input circuit IN, the diode D3, resistor R8, diode D4, the collector and emitter junction of transistor Q11, the base and emitter junction of transistor Q12, the resistor R20 and ground. As current now flows to the base of transistor Q11, it will be rendered conductive. When this occurs, capacitor C2 will be discharged over a path consisting of diode D4, the collector and emitter junction of transistor Q11 to ground. Thus, capacitor C2 becomes essentially short-circuited. The device Q4 will then be rendered non-conductive as the voltage across capacitor C2 falls below the value required to maintain the device Q4 conducive. As soon as device Q4 becomes non-conductive, the device Q5 will be turned off because no longer will current be supplied to the gate terminal G. Because the device Q5 is in series with the primary winding of transformer T2, current will no longer llow through the primary winding, whereupon the spark device SD will cease to function. Hence, there will be no longer any ignition of the gas supplied through the valve GV to the spark device SD.

At the moment when transistor Q12 becomes conductive, transistor Q10 also will become conductive Abecause of the addition of the voltage of resistor R20 to the series path through resistor R19 to the base of transistor Q10. Capacitor C6, which is part of the primary safety timer switch ST, will now discharge through a path established through the collector and emitter electrodes of transistor Q10. Capacitor C6 will be maintained in a discharged condition because the device Q10 remains conductive. Hence additional voltage will not reach capacitor C6. In other words, the primary safety timer circuit ST will be deactivated and rem-ain unoperated as long as the flame sensor FS detects a blue llame. However, as long as the primary safety timer circuit ST is disabled, the primary safety control network SC, which is ahead of the timer circuit ST, will remain operative and it will allow the motor MO to operate and the transformer T1 to supply sufficient voltage to maintain the gas admitted by valve GV to the spark device SD. The system will be retained in this status as long as the ame remains bluish in color.

It is also observed that the centrifugal switch CS, when closed, renders the device Q13 non-conductive because its anode is then connected to ground through the device Q2 of the prim-ary safety switch PS. Notwithstanding this, rectified current will still flow from the power control network CN through its resistor R2, then through diode D5 and resistor R16 to capacitor C5 to continue capacitor C5 in a charged condition. As long as the capacitor C5 remains so charged, the system will be in an operative l condition to maintain the flow of incoming gas even though the device Q13 has been switched out of the circuit.

The circuit of the thermostat TH will be opened in the usual manner as soon as there is no longer a demand for heat. When this happens, the gas valve GV will be deenergized, because of the higher impedance of transformer T3 in series with gas valve GV. Likewise, the fan timer FT will be deenergized. As soon as the gas valve GV is closed, however, the absence of gas will be accompanied by the extinction of flame at the spark device SD. The flame sensor FS will immediately detect an absence of flame, whereupon its own impedance, that is, the impedance of its principal component which may be a photoelectric conductor, will be rendered substantially high. Hence the transistor devices Q12 and Q11 of the flame detector network FN will become non-conductive in order. As soon as transistor Q11 becomes non-conductive, no current will flow through diode D4. Hence, the ignition circuit GC will again be energized, as already eX- plained, to render the system ready for re-operation in the event that the thermostat TH and the gas valve GV are reoperated. Furthermore, the primary safety timer circuit ST will be reenergized because transistor Q10 is also rendered non-conductive as already noted. Furthermore, upon the ignition circuit GC becoming activated, the heater coil HC is again supplied with current. The unidirectional charge on capacitor C6 will be reinstated. When sufficient voltage is developed across capacitor C6, the device Q9 will be rendered conductive, the conductivity path including capacitor C6, the device Q9, resistor R17, the base and emitter electrodes of transistor Q8 and and back to capacitor C6. The ow of base current to transistor Q8 will render that device immediately conductive, but transistors Q6 and Q7 will be rendered non-conductive. As already explained, this immediately renders the transistor Q1 conductive and the device Q2 will be turned off. At the same time, the similar device Q3 will be turned off. When the device Q3 is rendered non-conductive, the motor MO will be turned off. Likewise the ignition circuit GC will be rendered non-operative. The system is then completely turned off.

A special lock-out safety feature is incorporated in this system. Should there be a demand for heat so that the thermostat TH is activated and the gas pressure switch GS is also closed, the system would normally be expected to turn on. However, should there be a failure by which either the gas valve GV is disabled, or the ignition circuit GC fails to function, or any other failure occurs in the overall circuit and system, which might result in an absence of flame at the spark device SD, then the primary safety timer circuit ST will generate an output pulse at the collector of device Q8 and this generated pulse in time will trigger the primary safety control network SC so that it will turn off the device Q2, as previously explained. The device Q2 is the primary safety switch PS and, when it is non-conductive, it bars the system from going into operation. The system is locked-out. The system then can be restarted merely by resetting the thermostat TH if the system is otherwise in good operating condition.

A special feature involves rendering the system incapable of being re-started should there by any failure of operation of the basic control device Q2, which is the primary safety switch PS, at the end of a normal heating sequence. If the device Q2 becomes internally shorted, or if it fails to become non-conductive because there is a failure in any of the components of the power control network CN, or in the primary safety control network SC, or in the primary safety timer ST, or in the flame detector network FN, then the heater coil HC will be lactuated to open up the switch SS. In other words, the

switch SS will be opened up if the control current to the heater coil HC receives current for a sufficient or predetermined length of time. If the device SS is activated as just noted, its contacts will be opened and power will be completely removed from the burner system. The system can be reactivated only by manually resetting the secondary safety switch SS.

If the flame sensor FS were internally shorted prior to a demand for heat, then, according to this invention, the

system will be inoperative. In this case, let it be assumed.

that the thermostat TH becomes normally closed and that there is sufficient pressure in the gas main to hold switch GS closed. Capacitor C will be charged, but the voltage 8 to which the capacitor C5 becomes charged will be determined by the conductive states of devices Q11 and Q12 and the voltage across capacitor CS will not be sufficient to render transistor Q7 conductive. The primary safety control network SC will not be operated and no power can be transmitted to the system.

The system of this invention has been produced and it functioned satisfactorily as an ignition and monitoring system for oil or gas fired equipment installed on a roof top.

Another of the primary features of this invention involves the ability of the system to differentiate between a blue flame and a yellow ame. When there is a blue llame present, the ame sensor FS will exhibit an impedance of a substantially amount, such as, for example, 5000 to 10,000 ohms, but when a yellow ame is produced, the flame sensor FS, which, as already explained, may be a photo-conductive cell such as cadmium sulphide, will be rendered substantially conductive. The photo-conductive cell has a different spectral response to the two colors, being significantly greater for the yellow color than for the blue color. That is, its impedance will be negligible for the yellow ame. There is a substantial difference between the relative impedances between the blue flame condition and the yellow flame condition. As already stated, the capacitor C5 will be charged only to a voltage determined lby the states of the emitter-base junction of transistor Q12 and the base-emitter junction of transistor Q11. But the transistor Q7 will be rendered non-conductive, in turn rendering transistor Q6 non-conductive. Hence the device Q2 which is the primary safety switch PS will be turned olf. When this happens, the flame sensor FS detects an absence of flame, thereby increasing the resistance of the flame sensor FS and allowing the capacitor C5 to charge up to a larger voltage. The larger voltage on capacitor C5 will render the transistor Q7 conductive and in turn the device Q2 is also rendered conductive. This will turn the system on again. Hence, the system will oscillate and continue to oscillate in a relatively safe condition, turning the spark device SD on and off with each oscillation. However, the heater coil HC will in due course be activated for a suticient length of time and open its contacts SS, whereupon the ignition system will be disabled. Thus, the presence of the yellow flame for any substantial period of time will render the system non-operative. Except for a predetermined interval when the flame is yellow, the system will only operate continuously with a blue flame.

If the ame sensor FS is open-circuited, the primary safety timer ST will be enabled and the system will be turned olf.

Although this invention has been shown and described in particular embodiments merely for the purpose of illustration and explanation, it will be readily apparent to those skilled in the art that the features and the components of this invention are applicable to and may be embodied in a wide range of equipments without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. A power-operated direct ignition system for igniting fuel without a pilot light comprising means for producing a plurality of electrically generated sparks to ignite incoming fuel, sensor means for determining whether or not the flame produced by the ignited fuel is bluish in color, flame control means for interrupting the production of said sparks when the flame is changed to a substantially different color, and means responsive to a change to a substantially different color to fully remove power from the system so that it cannot be operated, said latter responsive means including a normally closed device coupling the source of power to the system and including also means for oscillating said flame control means and for operating said device for deenergizing the entire system when the flame control means is oscillated for a predetermined time interval.

2. A direct ignition system according to claim 1, in which the interrupting means actuates the spark producing means to produce a predetermined number of sparks before the llame is extinguished.

3. A direct ignition system according to claim 1, including, in addition, a main for feeding fuel to the vicinity of the spark producing means so that the fuel may be ignited, the interrupting means including means for closing the fuel main.

4. A power-operated direct ignition system for igniting fuel Without a pilot light comprising a thermostat for controlling the temperature at which the system will ignite the incoming fuel, a main for incoming fuel to be ignited, a spark producing device for producing continuously recurrent sparks to ignite the incoming fuel, a flame sensor for detecting the color of the ame of the ignited fuel, and apparatus coupled to said llame sensor and responding to a color different from a predetermined color in said ame for a predetermined time interval for interrupting the flow of fuel from said main and for substantially simultaneously interrupting the production of sparks by said spark producing device to extinguish said llame and for fully removing power from the system, said apparatus including a normally closed current responsive device which couples the power source to the system and which receives current when the llame sensor responds to a color dilferent from said predetermined color to deenergize the entire system.

5. A direct ignition system according to claim 4 in which the predetermined color is blue.

6. A direct ignition system according to claim 4 in which the interrupting apparatus, in responding to a color in said ilame different from the predetermined color, causes the spark producing device to produce several sparks before the flame is extinguished.

7. A direct ignition system according to claim 6 in which the flame sensor is a photo-cell.

8. A direct ignition system according to claim 7 in which the photo-cell is a cadmium sulphide element.

9. A direct ignition system according to claim 7 which responds to a llame outage within a predetermined time interval.

10. A direct ignition system according to claim 9 in which said predetermined time interval does not exceed approximately eight-tenths of a second.

11. A direct burner ignition system for igniting fuel without a pilot light, comprising a source of power for said system, a main for supplying fuel to be ignited, a

spark producer for recurrently producing sparks to ignite the incoming fuel, a thermostat having a circuit which may be closed for initiating the operation of the system, a gas pressure switch for rendering the fuel main operative only when the pressure within said main exceeds a predetermined value, a heater coil and bimetallic contacts controlled thereby for completely breaking the supply of power to the system when current ows through the heater coil for a predetermined time interval, a gas valve which is to be opened when the circuit of said thermostat is closed, and means for energizing the heater coil to break said bimetallic contacts for interrupting the operation of the system when there is an open-circuit condition or a short-circuit condition in the spark producer or in the flame sensor.

12. A direct burner ignition system for igniting fuel Without a pilot light according to the claim 11 comprising, in addition, a llame sensor responsive to the coloration of the flame produced by the ignited fuel, and means responsive to a flame coloration other than blue to interrupt the ilow of fuel to the system and to interrupt the production of sparks by the spark producer.

13. A direct burner ignition system for igniting fuel without a pilot light according to claim 12 in which, in addition, the interrupting means includes means for producing a predetermined group of sparks by the spark producer to interrupt the flow of fuel to the system and to interrupt the production of sparks by the spark producer.

14. A direct burner ignition system for igniting fuel without a pilot light according to claim 12 in which the flame sensor ncludes a cadmium sulphide cell.

15. A direct burner ignition system according to claim 11 in which a flame switch or a high temperature thermistor is employed to sense the presence of llame produced by the generated sparks.

References Cited UNITED STATES PATENTS EDWARD G. FAVORS, Primary Examiner 

